#main {
    width: 408px;
    height: 800px;
    background: white;
    border: 2px solid gray;
    margin: 0 auto;
    overflow: hidden;
}

h2 {
    text-align: center;
}

#con {
    width: 100%;
    height: 400px;
    position: relative;
    top: -400px; /*隐藏所有格子*/
    border-collapse: collapse;
}
/* 行 */
.row {
    height: 100px;
    width: 100%;
}
/* 一个块 */
.cell {
    height: 100px;
    width: 100px;
    float: left;
    /*border-left: rgb(54, 74, 129) 1px dashed;*/
    border: none;
}

.black {
    height: 50px;
    border-radius: 50%;
    background: rgba(0, 183, 255, 0.83);
}

.orange {
    height: 50px;
    border-radius: 50%;
    background: rgba(255, 145, 0, 0.89);
}

.btn {
    width: 100%;
    text-align: center;
}

.start {
    margin: 20px auto;
    width: 150px;
    height: 50px;
    border-radius: 10px;
    background: yellowgreen;
    line-height: 50px;
    color: #fff;
}

#con .row {
    position: relative;
    animation-name: exp;
    animation-duration: 0s;
    animation-timing-function: linear;
    animation-iteration-count: 8;

}

@keyframes exp {
    0%   {top: 0;opacity: 0;}
    25%  {top: 25px;opacity: 0.3;}
    50%  {top: 50px;opacity: 0.5;}
    75%  {top: 75px;opacity: 0.3;}
    100% {top: 100px;opacity: 0;}
}